Optical inspection systems can detect defects in inspected objects (such as printed circuit boards, wafers, masks and reticles) by illuminating an inspected object and processing images generated in response to the illumination.
Optical inspection systems for Printed Circuit Boards have to discriminate between materials. For example, these systems have to discriminate between insulators and conductors that are made of different materials. Each combination of insulator and conductive materials requires specific illumination conditions in order to obtain best image contrast.
Typical printed circuit board inspection systems use line based scanning that involves scanning a line of light over the printed circuit board. Line illumination does not illuminate features in a symmetrical manner.
There is a need to provide a system that illuminates a feature in a radial symmetrical manner.